This invention relates to an instantaneous water heater of the general type in which a fluid, usually water, is heated as it flows through a serpentine flow path and comes into contact with electric resistance heating elements. The particular disclosure of this application is of an instantaneous water heater with a redundant safety shut-off system responsive to either loss of fluid flow or excessive fluid temperature.
As the cost of fuel increases, it is becoming more economical to replace reservoir-type water heaters with instantaneous or "demand" water heaters which do not require storage of heated water for extended periods of time when not needed, and which heat water at the same rate as it is used so that no recovery time is required. Numerous types of instantaneous water heaters are known in the prior art and have been used in other parts of the world for many years. However, the relatively inexpensive cost of energy in the United States, combined with fears concerning the safety and reliability of instantaneous water heaters, has prevented this type of device from supplanting to any measurable degree older, reservoir water heaters.
For example, the Weinstein Pat. No. 3,261,963 discloses an automatic electric fluid heating apparatus which contains a plurality of resistance heating elements controlled in a pre-determined sequence by a motor-operated sequence switch with a built-in clutch control and a plurality of electro-mechanical relays. A reversible alternating current motor operates through a clutch to turn a shaft and a plurality of cams mounted thereon which engage and disengage contacts which in turn switch heating elements on and off. A fluid flow switch overrides the entire system when sufficient fluid is not being furnished to the heater. Weinstein and other patents, such as the Kaiser Pat. No. 3,531,622; Fuchslocher Pat. No. 3,370,154; and Flanders No. 3,952,182, all disclose instantaneous water heaters which, to the knowledge of applicant, have not achieved any degree of commercial success due to their complexity.